1. Field of the Invention
The present invention relates to a rotary vane compressor for an air conditioning system used in a vehicle such as an automobile, and more particularly, it relates to a variable displacement vane compressor which comprises a cylinder assembly including a cylindrical body having a bore and opposed end wall members secured to opposed ends of the cylindrical body, respectively, for closing the open ends of the bore, and a rotor disposed within the bore for rotation so as to form at least one crescent chamber between the rotor and the bore of the cylindrical assembly for receiving a refrigerant, the rotor having at least one vane which is extendably fitted in the rotor so that the free end of the vane is in contact with the circumferential inner wall surface of the bore during the rotation of the rotor, whereby, when the vane passes through the crescent chamber, the refrigerant introduced into the crescent chamber is adjusted in response to a change of a cooling load at the air conditioning system.
2. Description of the Related Arts
Conventionally, a variable displacement vane compressor of the above type is driven by an engine of the automobile, and the room temperature of the automobile is adjustable to a temperature at which a driver and passengers feel comfortable under ambient conditions. When a cooling load of the air conditioning system becomes high, the compressor must work at the maximum cooling capacity thereof, whereas when the cooling load becomes lower, the compressor preferably works at a lower cooling capacity. When the room temperature once reaches a comfortable temperature, the compressor preferably works at the minimum cooling capacity at which a comfortable temperature can be maintained.
U.S. patent application Ser. No. 902,311 (corresponding to Japanese Unexamined Patent Publication No. 60-193328) filed by the same applicant discloses an improvement of a variable displacement vane compressor of the above type, wherein a compression mode carried out by the vane is adjustable in response to a pressure change of the refrigerant within a suction chamber of the compressor, which is connected to an evaporator of the air conditioning system, whereby an amount of compressed refrigerant discharged from the compressor into the air conditioning system can be varied in response to a cooling load of the air conditioning system. Namely, this compressor comprises an annular plate member rotatably disposed between one of the end wall members of the cylinder assembly and the cylindrical body thereof. The annular plate member has an arcuate slot extending in the rotational direction of the vane and opening to the crescent chamber. The vane passes through the crescent chamber in such a manner that the vane divides the crescent chamber into a front and a rear section, with a volume of the front section being gradually decreased while a volume of the rear section is gradually increased. While the vane advances along the arcuate slot of the annular plate member, a part of the refrigerant received in the front section is allowed to escape into the rear section through the arcuate slot, and thus the compression mode starts just after the vane has passed through the arcuate slot of the annular plate member. With this arrangement, it is possible to adjust the compression mode by moving the annular plate member in the rotational direction of the vane in response to a pressure change of the refrigerant within the suction room of the compressor.
This movement of the annular plate member is caused by a spool member slidably accommodated in a cylindrical bore. The spool member divides the bore into two compartments, one of which (a first compartment) is always communicated with a discharging chamber into which the compressed refrigerant is discharged from the crescent chamber, and the other (a second compartment) receives a compression spring to bias the spool toward the first compartment and is communicated with a reservoir for lubricant oil pressurized to a pressure corresponding to that of the discharged refrigerant. The introduction of the oil into the second compartment is controlled by a check valve arranged midway in an oil path extending from the oil reservoir to the second compartment. The check valve operates in response to a change of the interior pressure of the suction chamber in such a manner that, when this pressure is lowered, the check valve allows a larger amount of the oil to flow into the second compartment and, conversely, when the pressure becomes higher, throttles the passage to limit the amount of the oil. The spool is displaced in the bore until a dynamic balance of the interior pressure between both compartments is attained, whereby the annular plate member is rotatably displaced in response to the movement of the spool. To obtain a proper displacement of the annular plate member, the interior pressure of the first compartment must be correctly maintained at a level corresponding to the interior pressure of the discharge chamber. The refrigerant (gas) filled in the second compartment, however, tends to leak therefrom to a lower pressure region in the compressor, mainly through an evitable micro-gap between a surface of the annular plate member and the associated surface of the end wall member in contact therewith. Thus, the dynamic balance of pressure between both the compartments is attained when the spool is displaced more to the first compartment side from the proper position.